This invention is related generally to the field of Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), Near field Scanning Optical Microscopy (NSOM), NanoSpectroPhotometry (NSP), NanoPolarimetry (NP), Magnetic Field Microscopy (MFM) and any other methods adaptable and suitable to guide the nanomachining techniques described herein. Specifically, the invention is directed to nanomachining techniques and apparatus, using AFM, NSOM, NSP, NP, MFM and STM technologies. These technologies are sometimes collectively referred to as Scanning probe Microscopy (SPM). Generally, SPM technologies allow one to “see” atomic-scale features on or in surfaces.
An AFM works by scanning a tip over a surface much the same way as a phonograph needle scans a record. The tip is located at the end of a cantilever beam and positioned over the surface to be scanned. The combination of the cantilever beam and tip is sometimes referred to collectively as a scanning probe or simply a probe.
AFM techniques rely on the effects of the inter-atomic interactions, such as van der Waals forces, that arise between the atoms in the structure of the tip and the atoms at the surface being imaged. As the tip is repelled by or attracted to the surface, the cantilever beam is deflected. The magnitudes of the deflections correspond to the topological features of the atomic structure of the surface being scanned. The AFM can work with the tip touching the sample (contact mode), or the tip can tap across the surface (tapping mode), or made to not touch the surface at all (non-contact mode—the preferred embodiment).
STM techniques rely on the fact that the electronprobability cloud associated with the atoms at the surface extends a very small distance above the surface as described by the quantum physical model. When a tip is brought sufficiently close to such a surface, there is an increadsingly stronger probability of an interaction (current) between the electron cloud on the surface and that of the tip atom. An electric tunneling current flows when a small voltage is applied. The tunneling current is very sensitive to the distance between the tip and the surface. These changes in the tunneling current with distance as the tip is scanned over the surface are used to produce an image of the surface.
AFM is being used to solve processing and materials problems in a wide range of technologies affecting the electronics, telecommunications, biological, chemical, automotive, aerospace, and energy industries. The materials being investigated include thin and thick film coatings, ceramics, composites, glasses, synthetic and biological membranes, metals, polymers, and semiconductors. The AFM is being applied to studies of phenomena such as abrasion, adhesion, cleaning, corrosion, etching, friction, lubrication, plating, and polishing.
The STM is widely used in both industrial and fundamental research to obtain atomic-scale images of surfaces. It provides a three-dimensional profile of the surface which is very useful for characterizing surface roughness, observing surface defects, and determining the size and conformation of molecules and aggregates on the surface.
A common image scanning technique involves vibrating a probe along the Z-axis as it is being translated in the X-Y plane about a surface of interest (STM is another common scanning technique, but is only suitable for conductive surfaces). The vibration is usually sinusoidal and maintained at a particular frequency. Typically, this frequency is the resonant frequency of the cantilever portion of the probe. An excitation energy is applied to the probe to create the vibratory motion, where the peak-to-peak deflection of the tip is determined by the level of the excitation energy. There are three common modes of operation: (1) the probe can work with the tip touching the surface (contact mode), (2) non-contact mode where the tip vibrates near the surface, and (3) the tip can tap across the surface (tapping mode). As the tip is scanned across the surface, the peak-to-peak deflection varies due to attractive forces between the constituent atoms of the tip and the atomic particles of the surface being scanned. An image of the surface is produced from variations in the resonance required to maintain a constant peak-to-peak deflection (e.g., using a feedback loop) by applying known image processing methods as is well known in the art.
Nanomachining involves removing material from a surface in a controlled manner to attain specific surface features. Typically, an appropriate scanning probe is manipulated so that its tip comes into contact with a surface to be nanomachined. The scanning probe is then translated along a pre-programmed vector, producing a scraping action across the contacted surface and removing an amount of material from the surface. An appropriate feed is applied to control the amount of material removed. This is repeated until the desired features are achieved. Any surface which is exposed to contact by the scanning probe can be nanomachined. Thus, for example the walls of a vertical structure can be nanomachined using a scanning probe having an appropriately shaped tip applied to the wall with an appropriate feed force. General techniques are more fully discussed in the various above-identified commonly owned U.S. patents and co-pending U.S. patent applications.
A commonly performed operation is the positioning of the scanning probe to locate the probe prior to making a cut. The process of locating involves scanning the surface to determine the position, for example by any of the techniques available to SPM and well known in the art. A side-effect of these scan methods is the physical alteration of the surface being scanned due to the contacting action of the probe tip upon the surface. This effect is sometimes referred to as “scan cutting.” Scan cutting can be disastrous for nanomachining purposes. Nanomachining techniques often involve making repeated motions along the same path. Consequently, the cumulative effect of scan cutting that would result during a nanomachining operation must be predictable and controlled.
When performing a nanomachining operation, it may be desirable to be able to verify or monitor the location of the surface as it is being machined. For example, if a recess is being formed into the surface of a workpiece, it might be desirable to confirm the depth of the recess. It might be necessary to monitor the progress of the nanomachining operation to detect when to stop the process. For example, nanomachining a workpiece comprising a multi-layered structure of different materials will likely progress at different rates due to varying hardness from one layer to the next. The ability to monitor the progression of the nanomachining operation allows appropriate control of the feedforce of the tip upon the surface to be nanomachined.
There is a need for techniques to improve nanomachining practices.